Current regulations for the burial of low level radioactive solid wastes require that the drainable liquid of a solid/liquid slurry in a burial container be less than 0.5% of the waste volume for a steel liner and less than 1% for a high integrity container. Regulations concerning high integrity containers further require that any apparatus internal to the burial container not cause the container to rupture during specified accident conditions.
Because any drain system in a burial container with a nuclear waste slurry would become contaminated during use, the preferred system would remain in the container for burial with the waste. This expendability dictates that the drain system itself occupy a relatively small volume and be inexpensive.
One current liquid removal system for steel liners utilizes precoated epoxy-sand filters that rest on the bottom of a waste burial container and draw liquid from the waste slurry through the epoxy-sand filter and out a conduit. The weight of this filter type demands that the filter underdrain be located on the floor of the container. The heavy support system needed for systems of this type are impractical in high integrity containers due to danger of container perforation during an accident.
The rate at which liquid is removed decreases as solids build up on the epoxy-sand filter underdrain. Due to the precoat, backflushing is impractical in that the precoat is destroyed during the backflush operation.
Desired is a separation system that, in addition to meeting the above regulations, is well distributed throughout the waste burial container for more homogeneous removal of liquid, and capable of being backflushed whenever solid accumulation on the filter elements restricts liquid flow.